Mis)interpreting supernovae observations in a lumpy universe
Mis)interpreting supernovae observations in a lumpy universe
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DOI：
10.1111/j.1365-2966.2012.21750.x
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发表时间：
2011-09
影响因子：
4.8
通讯作者：
C. Clarkson;G. Ellis;A. Faltenbacher;R. Maartens;Obinna Umeh;J. Uzan
中科院分区：
文献类型：
--
作者：
C. Clarkson;G. Ellis;A. Faltenbacher;R. Maartens;Obinna Umeh;J. Uzan
来自超新星等“点光源”的光被观测到，其光束宽度与光源大小的数量级相当--通常小于1Au。这样的束流探测器的物质和曲率分布与N体模拟或微扰理论中的粗粒度表示非常不同，后者在远大于1au的尺度上平滑。通常情况下，光束通过密度远低于宇宙平均密度的未聚集的暗物质和氢，并通过暗物质光晕和氢云。利用N体模拟和Press-Scheck hter方法，我们量化了密度概率分布作为束宽的函数，并表明，即使对于直径为500kpc的GPC长度的光束，大多数视线也明显密度不足。由此我们认为，对Au直径光束的概率分布进行建模是绝对关键的。标准分析预测，如此微小的光束尺寸会有巨大的变化，而非线性修正似乎不是微不足道的。甚至还不清楚密度不足的区域是否会导致光源变暗或变亮，因为我们显示的膨胀率是主要贡献，在模型中存在不确定性。通过考虑不同的合理近似产生非常不同的宇宙学，我们认为精确地模拟超窄光束仍然是精密宇宙学的关键问题。当将超新星观测与重子声振荡或宇宙微波背景距离进行比较时，这可能表现为角直径和光度距离之间的不一致。
Light from ‘point sources’ such as supernovae is observed with a beam width of the order of the sources’ size – typically less than 1 au. Such a beam probes matter and curvature distributions that are very different from coarse-grained representations in N-body simulations or perturbation theory, which are smoothed on scales much larger than 1 au. The beam typically travels through unclustered dark matter and hydrogen with a mean density much less than the cosmic mean, and through dark matter haloes and hydrogen clouds. Using N-body simulations, as well as a Press–Schechter approach, we quantify the density probability distribution as a function of beam width and show that, even for Gpc-length beams of 500 kpc diameter, most lines of sight are significantly underdense. From this we argue that modelling the probability distribution for au-diameter beams is absolutely critical. Standard analyses predict a huge variance for such tiny beam sizes, and non-linear corrections appear to be non-trivial. It is not even clear whether underdense regions lead to dimming or brightening of sources, owing to the uncertainty in modelling the expansion rate which we show is the dominant contribution. By considering different reasonable approximations which yield very different cosmologies, we argue that modelling ultra-narrow beams accurately remains a critical problem for precision cosmology. This could appear as a discordance between angular diameter and luminosity distances when comparing supernova observations to baryon acoustic oscillations or cosmic microwave background distances.